Python generic example

generic.py

from typing import TypeVar, Generic, List
import json

T = TypeVar('T')


class Stack(Generic[T]):
    def __init__(self) -> None:
        self.__items: List[T] = []

    def push(self, item: T) -> None:
        self.__items.append(item)

    def pop(self) -> T:
        return self.__items.pop()

    def empty(self) -> bool:
        return not self.__items

    def __str__(self):
        return json.dumps(self.__items)


a = Stack[int]()
a.push(3)
a.push(2)
a.push(1)
a.push('123')
a.push(123)
print(a)


# mypy generic.py
# generic.py:28: error: Argument 1 to "push" of "Stack" has incompatible type "str"; expected "int"